This invention is directed generally to the field of gear testing and more particularly to a novel and improved method and related apparatus for compensating for the contribution of master gear error in a gear checking apparatus.
Generally speaking, various gear testing or gear checking machines are known which utilize controlled apparatus for functional gear checking in which a highly accurate master gear is placed in mesh and rotated with the gear under test. Such gear checking machines rely on various methods and related apparatus to assure accuracy of the gear testing or checking carried out. For example, some testing machines depend upon precision drive motors and careful control of motor speeds for achieving gear checking. Other such apparatus rely on various electronic and electro-mechanical apparatus for determining various gear properties and tooth-to-tooth gear properties. All of these methods depend upon the controlled rotation of a gear under test in mesh with a highly accurate master gear.
One particularly useful type of gear checking apparatus is shown for example in U.S. Pat. No. 4,272,891 to Fusari, which is assigned to the assignee of this invention.
Generally speaking, gear testing instruments may be of the single flank or double flank variety. In the single flank type of gear testing apparatus, the master gear and gear to be tested are mounted for intermeshing in such a fashion that but one flank or side surface of each of the respective intermeshed gear teeth are in contact during the test, and the operating center-to-center distance is such that there is some "play" or what is known in the art as "backlash" between the intermeshed gear teeth. On the other hand, double flank testing systems incorporate a "floating" axis which is arranged so as to maintain some pressure of engagement between the gears in such a fashion as to maintain the respective gear teeth more fully intermeshed, such that each gear tooth of the master gear, for example, constantly engages the adjacent faces or surfaces of the gear teeth of the gear under test to either side thereof.
The foregoing Fusari patent utilizes an instrument and fixture for generating an analog type of signal corresponding to relative center-to-center movement experienced between the intermeshed gears due to irregularities or imperfections in the gear to be tested. These analog signals may be further processed by either analog or digital circuits to obtain desired quantities indicative of various composite properties of the gear under test or of individual tooth-to-tooth variations. On the other hand, some gear testing apparatus utilize analog-to-digital conversion of the signals at an early stage, relying upon digital signal processing thereafter to extract the desired quantities relative to the properties of the gear under test.
However, most of the prior art gear testing apparatus have heretofore assumed that all variations in gear rotation are due to irregularities or imperfections in the "test gear" or gear under test. That is, a highly accurate, precision master gear has been utilized in the test fixture for intermeshing with the test gear, such that it can be assumed that irregularities observed are due to imperfections in the latter. Such highly accurate, precision master gears are of course relatively difficult and expensive to produce. Moreover, even with such accurate gears, some slight inaccuracies, irregularities or imperfections may nonetheless occur. Moreover, wear and/or damage over a period of service may introduce such irregularities or inaccuracies into the precision master gear.
Accordingly, it is often the practice to remove and replace the master gear after a given period of time and/or after a given number of test gears have been checked by the master. Such replacement is relatively time-consuming and expensive.
The present invention proposes a novel method and system for both determining and compensating for master gear error in such a gear checking apparatus. Hence, the present invention obviates the necessity for providing extemely accurate precision master gears at great expense, since any errors or imperfections in the master gear can be compensated for by the apparatus and method of the invention. Moreover, the present invention makes possible periodic rechecking and recalculation of master gear error, so as to accommodate changes in master gear configuration which may occur due to wear and/or damage over a period of use.